In certain vehicles, an operator may customize the level of audible exhaust noise via a user interface. Based on the input from the operator, a position of an exhaust tuning valve is adjusted to regulate the level of audible exhaust noise. However, an operator may not frequently change the desired level of exhaust noise and may select a constant level of noise. The exhaust tuning valve may exhibit degradation over time. The presence of degradation in the tuning valve may reduce the ability to adjust the level of audible noise as desired, thereby adversely affecting the driving experience.
Various approaches are provided for carrying out diagnostics of exhaust system valves. In one example approach, as shown in U.S. Pat. No. 8,543,288, Bligard et al. shows a diagnostic method for an exhaust gas pressure regulator (butterfly flap) in an exhaust system connected to a turbocharged internal combustion engine to be carried out during engine braking. The method includes, demanding engine brake, measuring back pressure in exhaust by a back pressure sensor when demanding engine brake, measuring boost pressure by a boost pressure sensor when demanding engine brake, and then comparing the measured back pressure and boost pressure to determine if there is fault in the pressure regulator or the backpressure sensor.
However, the inventors herein have recognized potential disadvantages with the above approach. As one example, the diagnostic routine described above is carried out during engine combustion conditions. However, such an approach may not be suitable for carrying out diagnostics of the exhaust tuning valve, since the driving experience may be adversely affected due to undesirable variations in exhaust noise as perceived by the operator. For example, if an operator selects a constant exhaust noise level, such as with the exhaust tuning valve in a closed position, the position of the exhaust tuning valve may not be altered and during the drive cycle, diagnostics of the exhaust tuning valve may not be carried out corresponding to each position of the valve. Therefore, if the valve is stuck at a certain position (such as a completely closed position), it may not be possible to detect degradation of the valve. Further, adjustment of the position of the exhaust tuning valve may not result in a sufficiently high enough change in exhaust backpressure to detect degradation during all driving conditions.
The inventors herein have recognized that the issues described above may be addressed by an engine method comprising: during unfueled cranking of an engine while the engine is spun in reverse, varying a position of an exhaust tuning valve, and diagnosing the exhaust tuning valve based on an intake air flow at one or more positions of the exhaust tuning valve. In this way, by opportunistically reverse spinning the engine during a vehicle key-off condition and varying the position of the exhaust tuning valve, degradation of the exhaust tuning valve may be diagnosed based on intake air flow corresponding to each position of the exhaust tuning valve.
As one example, an exhaust tuning valve such as a butterfly valve may be positioned in an exhaust bypass passage across a muffler to control backpressure in the system and/or exhaust flow through the muffler. Based on a level of exhaust noise desired by the operator, as indicated via an on-board human-machine interface (HMI), a position of the tuning valve may be adjusted to regulate exhaust flow via the tuning valve and the muffler. The engine may comprise a battery operated electric booster used for providing additional boost during increased torque demand. A diagnostic routine of the exhaust tuning valve may be opportunistically carried out during vehicle key-off conditions when the engine is not operated and the vehicle is unoccupied. The diagnostic routine includes rotating the engine in a reverse direction via an electric machine and also spinning the electric booster in a reverse direction to draw in ambient air from the tailpipe and route the air to the intake manifold. While the engine is spinning, the opening of the exhaust tuning valve is continually varied from a fully open position to a completely closed position. At each position of the exhaust tuning valve, air flow via the intake manifold may be estimated based on input from a manifold air flow (MAF) sensor. If the MAF reading changes proportionately with an increase in the exhaust tuning valve opening from a fully open position to a fully closed position, it may be confirmed that the exhaust tuning valve is not degraded. If the MAF reading is not directly proportional to the degree of opening of the exhaust tuning valve, it may be confirmed that the valve is degraded and a flag may be set.
In this way, even if there is no change in the desired exhaust noise level over a period of time, the diagnostics for the exhaust tuning valve may be opportunistically carried out at each position of the valve. By using existing engine components such as the electric booster and the MAF sensor for detecting degradation of the exhaust tuning valve, additional components are not required, thereby providing cost and components benefits. The technical effect of carrying out the diagnostics during an engine non-combusting condition is that even as the position of the exhaust tuning valve is altered, since the vehicle is not combusting, undesirable noise is not produced during the diagnostic routine. Overall, by regularly monitoring the health of the exhaust tuning valve, operator regulation of audible exhaust noise may be maintained and driving experience may be improved.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.